288 



FINE-STRUCTURE OF PROTOPLASMIC DERIVATIVES 



III 



c 

 o 



50 



- 40 



- 30 



- 20 



- W 



■c 



c 

 J' 



400 



300 



200 



o 

 S 



o 



e 



CO 



o 

 40 



30 



20 



favourably with those of the 9 mm coleoptile; a real increase per mm 

 occurs for lipids, pectins and above all for cellulose, which is compen- 

 sated by a loss in proteins and ash. This investigation proves that cell 

 elongation is accompanied by a most intense metabolism^. Osmotic 

 phenomena are only accessory manifestations of that metabolism; they 

 are never the cause of any growth. 



BuRSTROM (1942) has carefully studied the osmotic conditions 



during cell elongation in wheat 

 QOnjAt root. It is seen from Fig. 142 that 

 the turgor pressure temporarily 

 decreases during the lengthening 

 of the cell. To raise it to its initial 

 level, osmotic material has to be 

 brought into the cell. Since ener- 

 gy is required to transport ma- 

 terial (Arisz, 1943), there must 

 be considerable respiration dur- 

 ing the elongation of the cell 

 (Bonner, 1936b). This proceeds, 

 therefore, not only by means of 

 osmotically accumulated poten- 

 tial energy, but chemical respira- 

 tory energy is needed as well. 

 Turgor extension is at its greatest 

 at the moment when turgor 

 pressure is at its lowest, from 

 which it follows that the wall 

 then has its maximum elasticity 

 (Frey-Wyssling, 1948 a, b). Af- 

 terwards elasticity is obviously 

 reduced by the stiffening of the 

 new wall areas (Fig. 140a, p. 284). 

 It is curious that, despite the 

 turgor, the stretchable bipolar 

 cell outgrowths show no tendency to become spherical during the ex- 

 tension. This is due to the submicroscopic tubular texture of the cells, 



1 BuRSTROM (195 1) produces evidence showing that cell elongation and increase of dry 

 matter are nevertheless physiologically separated processes. 



m -10 







10 



20 



Time units 



Fig. 142. Osmotic conditions during the 

 elongation growth of single cells in wheat 

 root (compounded from various illustrations 

 in BuRSTROM, 1942). Abscissa: Time (time 

 unit is duration of mitosis in the tip of the 

 root). Ordinates: a) Length of cell in^; 

 b) turgor extension in yu ; c) turgor pressure 

 in at.; d) osmotic material per cell in (lo//)^ 

 times at. (From Frey-Wyssling, 1945 a). 



